Benchmarking wood waste combustion

Background

Wood combustion plant >0.4 MW requires local authority authorisation and is controlled under process guidance note PG1/12. It is believed that these requirements affect around 275 sites, the vast majority of which are furniture manufacturers. Authorised combustion plant must comply with the requirements of the guidance note.

During the review of the process guidance note in 1999, it become very apparent that there were many gaps in our knowledge of the scale and state of authorised wood combustion. In addition, there were also large variations in operational practices and the subsequent levels of emissions generated by similar plants.

Therefore, BFM Ltd conducted this project on Benchmarking wood waste combustion to fill these information gaps.

• The final project report can be downloaded here

Project aims

• Quantify the variables associated with wood combustion
  Information would be gathered on the number of authorised plant in the UK, volume of material burned, energy generated / used and the sectoral emissions.

• Produce a best practice document
  This would contain benchmarking information on boiler performance to allow manufacturers to compare their own practices / emissions with those of the best. Best practice advice would be provided on system optimisation along with the provision of guidance on the size / costs / paybacks of different systems. The latter would show companies the calculations needed to evaluate the viability of a new wood combustion system

• Report findings to a wide audience
  The best practice publication would be circulated free-of-charge to companies with an interest in wood combustion. The results would also be fed into the review of PG1/12.

Executive summary

On-site combustion is the single most important waste management option for wood waste from the furniture manufacturing sector. This study suggests that combustion in authorised wood burning boilers accounts for 223,500 tonnes of waste wood from the furniture sector each year. The option is particularly attractive for companies which process board material, due to the lack of off-site uses for the associated waste coupled with the cost of landfill which can be up to £70 per tonne.

Plant specified at 0.4 MW to 3 MW thermal input, requires authorisation by the local regulator. Such plant typically consumes between 90 and 675 kg/hour of wood waste and this study estimates that there are probably around 275 such units in the UK. Initial installation costs normally range between £100,000 and £500,000 for a complete package and a lifespan of 20 to 30 years can be expected.

Controls are laid out in process guidance note PG1/12(04). Of particular significance are the emission limits which apply to carbon monoxide and particulate matter, which are complied with by 50% and 51.9% of companies respectively. Other limits apply to formaldehyde (85.7%), hydrogen chloride (94.9%), hydrogen cyanide (74.3%) and organic compounds (72.2%). Scope exists to improve these emissions through attention to fuel consistency, combustion temperature, residence time, turbulence and oxygen.

There is also potential to make better use of the energy generated by this combustion. All of the systems in this study generated heat rather than heat and electricity. The lack of process heat requirements typically meant that the majority of the energy was simply dissipated heat to atmosphere during 7 or 8 months of the year. Examples have been provided of Continental initiatives for combined heat and power plants, district heating schemes and the opportunity for the sale of process heat &/or cooling to neighbouring factories.

With the commitment, skills and expertise of both organisations, Biffaward has grown in stature and reputation, resulting in one of the most respected landfill tax credit funded schemes.